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Position correction in sodar and meteorological lidar systems

Position correction in sodar and meteorological lidar systems description/claims

This application is a continuation in part of application Ser. No. 11/934,915 filed on Nov. 5, 2007. This application is also a continuation in part of application Ser. No. 12/117,994 filed on May 9, 2008. This application is also a continuation in part of application Ser. No. 12/125,166 filed on May 22, 2008. The entire disclosures of these three applications are incorporated herein by reference. This application also claims priority of Provisional Patent Application Ser. No. 60/941,387, filed on Jun. 1, 2007, the entire disclosure of which is incorporated herein by reference.

The present invention relates to a system for remotely detecting atmospheric phenomena such as wind speed using either directed sound waves or laser beams.

Sodar systems employ directed sound waves to detect atmospheric phenomena such as wind speed. Meteorological lidar systems use laser beams for the same purpose. The apparatuses housing the active transducers of these systems are generally deployed in fixed, carefully oriented positions in the field, such that the angles of emitted and detected signals have known relations to vertical and horizontal coordinates. Usually this requires leveling the platform upon which the transducers are mounted, and turning the platform such that it is aligned with a compass point, e.g., due north. Such systems calculate wind speeds and directions based on the prerequisite fixed orientation of the transducers.

Wind speed measurements made for the purposes of wind energy resource assessment are expected to be rather accurate; typically ±0.5 mph (approximately ±0.23 m/s). As such, the errors that would be introduced by tilting of the apparatus of only a few degrees are important to correct in this application. Additionally, at many sites wind speed can vary to an extent which significantly affects the economic viability of a potential wind turbine installation over a very short geographic distance. As a result, precise and accurate information regarding the location at which a measurement for wind energy was made is essential.

Existing and near future wind energy installations are on dry land or near-shore sea locations. Resource assessment equipment for such sites can and has been mounted on stable foundations on land and on the near-shore seabed. Resource availability and other siting issues related to these terrestrial and near-shore sites are motivating research, including resource assessment studies, into deeper water installations where fixed foundations are prohibitively expensive. Buoy, barge, or ship mounted wind measurement equipment, typically used to measure wind velocity in such locations, is inadequate for resource assessment in several respects. The measurements are typically made within a few meters of the sea surface, while resource assessment data is preferably taken at turbine hub height, typically 60-110 meters above the sea surface for modern utility scale turbines. Further, the accuracy of conventional anemometry mounted on floating structures is adversely affected by the motion of these structures. Also, the location of these sensors relative to their support structures is often such that the structures adversely affect accuracy by influencing the airflow. Finally, in particular for ship-based measurements, the duration of measurement is inadequate for resource assessment, where measurement periods of up to a year or more are considered necessary for accurate resource assessment.

To date no sodar or lidar equipment has been built which is suitable for making measurements sufficiently accurate for resource assessment on non-stationary structures.

In one embodiment, the invention comprises sensors in the sodar or lidar systems that detect the apparatus orientation and position, and operational software (“firmware”) that uses at least the sensed orientations to adjust in situ the calculations of wind speeds and directions in three dimensions for deviations from some nominal orientation, such that the accuracy of the measurements is not degraded. The firmware performs the calculations in real time, based on orientation and position information measured on a continuing basis to maintain reliable data accuracy even in the presence of post-installation orientation or position shift of the system which might otherwise degrade data accuracy. Further, data structures identifying the algorithm used to correct for the orientation and position of the system, and the orientation and position data serving as the input to this algorithm, are included with all collected, transmitted, and archived data for documentary purposes.

One of the benefits of the inventive orientation compensation is that the sodar or lidar apparatus need not be oriented precisely at the time of installation. Further, installation time is reduced, since precise orientation can be tedious. Also, the apparatus need not have a finely adjustable leveling mechanism, nor does the apparatus need to be installed on level ground. Even if it may be securely anchored or guyed to the ground, minor shifting or settling of the apparatus may occur as a result of wind loading, ground settling due to precipitation, or other environmental factors. By continually monitoring apparatus orientation and position, data remains reliable despite such movements. The invention can compensate for the expansion or contraction of the sodar or lidar apparatus with ambient temperature changes that can be of sufficient magnitude to affect the accuracy of the orientation, especially with plastic structures which may be economical and expedient for other reasons.

Also, there may be site obstructions that interfere with signal transmission or detection, which can be avoided by orienting the apparatus as needed. In the case of floating sodar or lidar systems, platform motion can be accounted and corrected for. Also, the invention generally increases the confidence level of all transmitted and/or collected data. Further, compared against competitive apparatuses which may report, but not automatically compensate for, orientation and positioning errors, the invention reduces or eliminates the need for post-processing orientation correction of the data. Additionally, geographic position information derived from a Global Positioning System receiver “GPS” built into the instrument can be used to identify with certainty the location at which the measurements are being made and to compensate for errors in the electronic compass by automatically including the effects of known location-specific magnetic anomalies, which have been mapped and for which data is available.

This invention features a system for correcting wind speed and direction data collected by a sodar or lidar apparatus for at least the orientation of the apparatus, comprising one or more sensors mounted to the sodar or lidar apparatus that detect at least the three-dimensional angular orientation of the apparatus, and software that uses the detected three-dimensional angular orientation to adjust in situ the calculations of wind speed and direction data in three dimensions for deviations from some nominal orientation.

The system may further comprise one or more additional sensors mounted to the apparatus that detect the position of the apparatus. The system may further comprise software and data structures that cause the inclusion of data indicative of the orientation and position of the apparatus with the collected data. The software may perform the calculations in real time, based on orientation measured on a continuing basis to maintain reliable data accuracy even in the presence of post-installation positional shift of the apparatus which might otherwise degrade data accuracy.

The directional orientation may be measured with an electronic two or three axis compass, and tilt from vertical may be measured with a two axis accelerometer-based inclinometer. The system may further comprise a third accelerometer axis. The system may further comprise one or more gyroscopes or other angular acceleration measurement sensors to also account for angular motion of the apparatus, along with motion along horizontal axes, to properly distinguish between angular inclinations and axial accelerations of the apparatus to correct for dynamic motions of the apparatus. The system may further comprise a GPS receiver that is used to measure the position of the apparatus. The GPS receiver may also measure directional orientation.

Also featured is a method of correcting wind speed and direction data collected by a sodar or lidar apparatus for at least the orientation of the apparatus, comprising detecting at least the three-dimensional angular orientation of the sodar or lidar apparatus, and using the detected three-dimensional angular orientation to adjust in situ the calculations of wind speed and direction data in three dimensions for deviations from some nominal orientation.

The method may further comprise detecting the position of the apparatus. The method may further comprise causing the inclusion of the orientation and position information of the apparatus with the collected data. The software may perform the calculations in real time, based on orientation measured on a continuing basis to maintain reliable data accuracy even in the presence of post-installation position or angular shift of the apparatus which might otherwise degrade data accuracy. Directional orientation may be measured with an electronic two or three axis compass, and tilt from vertical is measured with a two axis accelerometer-based inclinometer.

Angular accelerations, velocities and orientation of the apparatus may be measured using one or more gyroscopes, solid-state gyroscopes, or other angular measurement sensors to properly distinguish between angular inclinations and axial accelerations of the apparatus to correct for dynamic motions of the apparatus. The position of the apparatus may be measured using a GPS receiver. The GPS receiver may also measure directional orientation of the apparatus. Software may perform the calculations based on information provided at least in part by a user. In one embodiment, the user can override the detection of one or more of the orientation and position of the apparatus, so that the software performs the calculations based on information provided at least in part by a user.

Also featured is a method of correcting wind speed and direction data collected by a sodar or lidar apparatus for the orientation and/or position of the apparatus, comprising providing the three-dimensional angular orientation of the sodar or lidar apparatus, and using the provided three-dimensional angular orientation to adjust in situ the calculations of wind speed and direction data in three dimensions for deviations from some nominal orientation. The three-dimensional angular orientation may be provided at least in part with one or more instruments coupled to the sodar or lidar apparatus, and may be provided at least in part by a user who has overridden the instruments. Alternatively, the three-dimensional angular orientation may be provided by a user. The method may further comprise detecting failures of the one or more instruments, and in which the last valid orientation information is used to adjust the calculations of windspeed and direction.

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• Utility Patent

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